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Cooling of TF

Transformers generate heat due to iron and copper losses, requiring efficient heat dissipation to prevent overheating, primarily through conduction, convection, and radiation. Cooling transformers is more complex than cooling rotating machines due to the lack of moving parts, with oil being a preferred coolant for its thermal properties and electrical insulation. Various cooling methods are categorized by the cooling agent and circulation method, including oil-immersed and air cooling techniques tailored to different transformer sizes and load capacities.

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Sibgatullah Wadho
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38 views3 pages

Cooling of TF

Transformers generate heat due to iron and copper losses, requiring efficient heat dissipation to prevent overheating, primarily through conduction, convection, and radiation. Cooling transformers is more complex than cooling rotating machines due to the lack of moving parts, with oil being a preferred coolant for its thermal properties and electrical insulation. Various cooling methods are categorized by the cooling agent and circulation method, including oil-immersed and air cooling techniques tailored to different transformer sizes and load capacities.

Uploaded by

Sibgatullah Wadho
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Introduction to Heat Transfer in Transformers

Transformers generate heat due to iron losses and copper


losses during operation. This heat must be dissipated efficiently to
prevent overheating and ensure reliable performance. The heat
transfer occurs through three primary mechanisms:
The primary methods of heat transfer involved are:
• Conduction: Heat transfer through the solid parts of the
transformer, such as the core, windings, and insulation.
• Convection: Heat transfer from the transformer's surface to a
coolant fluid (like oil or air), causing the fluid to circulate.
• Radiation: Heat transfer through electromagnetic waves from
the transformer to its surroundings

Transformer Cooling Challenges


Cooling transformers is more challenging than cooling rotating
machines because transformers lack moving parts to assist coolant
circulation
Natural Circulation in Oil-Cooled Transformers
• Oil inside transformer absorbs heat through conduction from
windings and core.
• Heated oil becomes lighter and rises.
• It moves to radiators or external surfaces, where air or water
removes the heat.
• As it cools, it contracts and sinks, completing the circulation
loop.
Oil is chosen because it:
• Has high thermal expansion, enhancing circulation.
• Is a good electrical insulator, adding an extra safety layer.
The cooling methods are categorized by the cooling agent used (oil,
air, or water) and the circulation method (natural or forced).
Here's a breakdown of the cooling methods discussed:
• Oil Immersed, Oil Cooling:
o ONAN (Oil Natural Air Natural): This method uses natural
circulation of oil and air to cool the transformer and is
common for transformers up to 5 MVA.
o ONAF (Oil Natural Air Forced): This method is similar to
ONAN, but uses fans to force air circulation when the
temperature rises. This allows the transformer to handle
higher loads than with ONAN alone.
o OFAF (Oil Forced Air Forced): This method uses pumps for
forced oil circulation and fans for forced air circulation,
providing more effective cooling for higher-rated
transformers.
o ONWF (Oil Natural Water Forced): This method uses
natural oil circulation and forced water circulation through
cooling coils inside the transformer tank.
o OFWF (Oil Forced Water Forced): This method uses both
forced oil and water circulation with an external heat
exchanger to cool the transformer.
• Air Cooling:
o AN (Air Natural): This method uses natural air circulation
to cool the transformer and is suitable for smaller
transformers up to 1.5 MVA.
o AF (Air Forced): This method uses forced air circulation to
improve heat dissipation and is used for transformers up
to 3 MVA

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